The present invention relates to the field of abrasive tool inserts and, more particularly, to such inserts having a support having a sawtooth pattern of concentric rings having superimposed radially outwardly sloping troughs extending from the center of the support to its periphery and wherein the profile of the substrate from its center to its periphery slopes downwardly.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. An abrasive particle compact is a polycrystalline mass of abrasive particles, such as diamond and/or cubic boron nitride (CBN), bonded together to form an integral, tough, high-strength mass. Such components can be bonded together in a particle-to-particle self-bonded relationship, by means of a bonding medium disposed between the particles, or by combinations thereof. The abrasive particle content of the abrasive compact is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are made under elevated or high pressure and temperature (HP/HT) conditions at which the particles, diamond or CBN, are crystallographically stable. For example, see U.S. Pat. Nos. 3,136,615, 3,141,746, and 3,233,988.
A supported abrasive particle compact, herein termed a composite compact, is an abrasive particle compact, which is bonded to a substrate material, such as cemented tungsten carbide.
Abrasive compacts tend to be brittle and, in use, they frequently are supported by being bonded to a cemented carbide substrate. Such supported abrasive compacts are known in the art as composite abrasive compacts. Compacts of this type are described, for example, in U.S. Pat. Nos. 3,743,489, 3,745,623, and 3,767,371. The bond to the support can be formed either during or subsequent to the formation of the abrasive particle compact. Composite abrasive compacts may be used as such in the working surface of an abrasive tool.
Composite compacts have found special utility as cutting elements in drill bits. Drill bits for use in rock drilling, machining of wear resistant materials, and other operations which require high abrasion resistance or wear resistance generally consist of a plurality of polycrystalline abrasive cutting elements fixed in a holder. Particularly, U.S. Pat. Nos. 4,109,737 and 5,374,854, describe drill bits with a tungsten carbide stud (substrate) having a polycrystalline diamond compact on the outer surface of the cutting element. A plurality of these cutting elements then are mounted generally by interference fit into recesses into the crown of a drill bit, such as a rotary drill bit. These drill bits generally have means for providing water-cooling or other cooling fluids to the interface between the drill crown and the substance being drilled during drilling operations. Generally, the cutting element comprises an elongated pin of a metal carbide (stud) which may be either sintered or cemented carbide (such as tungsten carbide) with an abrasive particle compact (e.g., polycrystalline diamond) at one end of the pin for form a composite compact.
Fabrication of the composite compact typically is achieved by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate and compressed under HP/HT conditions. In so doing, metal binder migrates from the substrate and "sweeps" through the diamond grains to promote a sintering of the diamond grains. As a result, the diamond grains become bonded to each other to form a diamond layer, which concomitantly is bonded to the substrate along a conventionally planar interface. Metal binder can remain disposed in the diamond layer within pores defined between the diamond grains.
A composite compact formed in the above-described manner may be subject to a number of shortcomings. For example, the coefficients of thermal expansion and elastic constants of cemented carbide and diamond are close, but not exactly the same. Thus, during heating or cooling of the polycrystalline diamond compact (PDC), thermally induced stresses occur at the interface between the diamond layer and the cemented carbide substrate, the magnitude of these stresses being dependent, for example, on the disparity in thermal expansion coefficients and elastic constants.
Another potential shortcoming, which should be considered, relates to the creation of internal stresses within the diamond layer, which can result in a fracturing of that layer. Such stresses also result from the presence of the cemented carbide substrate and are distributed according to the size, geometry, and physical properties of the cemented carbide substrate and the polycrystalline diamond layer.
Recently, various PDC structures have been proposed in which the diamond/carbide interface contains a number of ridges, grooves, or other indentations aimed at reducing the susceptibility of the diamond/carbide interface to mechanical and thermal stresses. In U.S. Pat. No. 4,784,023, a PDC includes an interface having a number of alternating grooves and ridges, the top and bottom of which are substantially parallel with the compact surface and the sides of which are substantially perpendicular to the compact surface.
U.S. Pat. No. 4,972,637 proposes a PDC having an interface containing discrete, spaced-apart recesses extending into the cemented carbide layer, the recesses containing abrasive material (e.g., diamond) and being arranged in a series of rows, each recess being staggered relative to its nearest neighbor in an adjacent row. It is asserted in the '637 patent that as wear reaches the diamond/carbide interface, the recesses, filled with diamond, wear less rapidly than the cemented carbide and act, in effect, as cutting ridges or projections. When the PDC is mounted on a stud cutter, as shown in FIG. 5 of the '637 patent, wear plane 38 exposes carbide regions 42, which wear more rapidly than the diamond material in the recesses 18. As a consequence, depressions develop in these regions between the diamond filled recesses. The '637 patent asserts that these depressed regions, which expose additional edges of diamond material, enhance the cutting action of the PDC.
U.S. Pat. No. 5,007,207 proposes an alternative PDC structure having a number of recesses in the carbide layer, each filled with diamond, which recesses are formed into a spiral or concentric circular pattern (looking down at the disc shaped compact). Thus, the '207 structure differs from the '637 structure in that, rather than employing a large number of discrete recesses, the '207 structure uses one or a few elongated recesses which form a spiral or concentric circular pattern. FIG. 5 in the '207 patent shows the wear plane, which develops when the PDC is mounted and used on a stud cutter. As with the '637 structure, the wear process creates depressions in the carbide material between the diamond filled recesses in the '207 structure. Like the '207 patent, the '637 patent also asserts that these depressions, which develop during the wear process, enhance cutting action.
U.S. Pat. No. 5,484,330 proposes an abrasive tool insert wherein the carbide support forms a sawtooth shaped cross-sectional profile that includes a number of surfaces sloping outwardly and downwardly toward a cutting edge of the insert.
U.S. Pat. No. 5,486,137 proposes an abrasive tool insert having an abrasive particle layer having an upper surface, an outer periphery, and a lower surface integrally formed on a substrate which defines an interface therebetween. The abrasive particle layer outer periphery forms a cutting plane. The thickness of the abrasive particle layer at its outer periphery cutting plane decreases radially inwardly. Thus, the interface can have a sawtooth shape cross-sectional profile, at least one slot extending from said abrasive particle layer outer periphery radially inwardly, or other configuration based on the precepts of the present invention. Also, the angle of the outwardly sloping profile can be matched to the anticipated angle of the wear plane, which will develop as the PDC wears in use.
U.S. Pat. No. 5,494,477 proposes an abrasive tool insert comprises a cemented substrate and a polycrystalline diamond layer formed thereon by high pressure, high temperature processing. The interface between the substrate and the diamond layer comprises at least one angled profile wherein said profile slopes downwardly and outwardly toward the periphery of the insert.
Whereas the aforementioned patents assert a desirable cutting action in the rock, it is also highly desirable to minimize the diamond layers susceptibility to fracture and spall which in part arises from the internal residual stresses.
Accordingly, it would be highly desirable to provide a polycrystalline diamond compact having increased resistance to diamond spalling fractures.